High frequency radio tube



June 30, 1942. A. K. wms, JR 2,288,330

HIGH FREQUENCY RADIO TUBE Filed Jan. 2, 1941 iiiiiiiiiiiiiiiiii umuuu!!INVENIOR. I A. K. WING, JR.

I BY m zz.

ATTORNEY.

Patented June 30, 1942 2,288,880 man FREQUENCY more runs Arthur K. Wing,In, Chatham, N. 1., asslgnor to Radio Corporation of America, acorporation of Delaware Application January 2, 1941, Serial No. 372,867

Claims.

My invention relates to electron discharge devices, particularly totransmitter tubes for high frequency operation.

Conventional structures and methods of assembly cannot be used in makingtransmitter tubes suitable for amplifier operation at high frequencysuch as in television and frequency modulation transmitters where thefrequency may be higher than 30 or 40 megacycles and where the power maybe several kilowatts. The close spacing of the electrodes requiresaccurate alignment and rigid support and the intense high frequencyfields require complete electrostatic isolation of the output and inputcircuits and electrodes. It is desirable to keep the mass of the metalparts of the tube at a minimum.

The object of my invention is an improved radio tube of the transmittertype in which the electrodes are accurately aligned and rigidlysupported with a minimum of metal mass, and in which the outputelectrodes are completely shielded from the input electrodes.

The characteristic features of my invention are defined in the appendedclaims and the preferred embodiment thereof is described in thefollowing specification and shown in the accompanying drawing in whichFigure 1 is a longitudinal half-section of my improved tube, Figure 2 isa sectioned detailed view taken along line 2-2 of Figure 1 showing thecathode support, and Figure 3 is a view along the line 3-3 of Figure 1.

The anode I is of the externally cooled type and encloses coaxial screengrid 2, control grid 3 and cathode 4. The two grids are cylindrical,each comprising a. plurality of parallel grid wires arranged in a circleand held at their ends by collars. The cathode shown comprises a singlehelix of electron emissive metal such as tungsten or thoriated tungstensupported at its upper end on the central rod 5, the rod being joined atits lower end to the bridge structure 6 which in turn-is clamped at itsopposite ends to the two lead-in conductors 1 for the cathode. Thecontrol grid lead-in conductors, not visible in Figure l, are of thesame size and shape as the cathode lead-ins and are in a plane normal tothe plane of the cathode lead-ins. The four bushings 8 for the lead-inconductors comprise, preferably, joined at one end to a metal disc andat the other end to a metal sleeve, which is in turn brazed to openingsin the sheet metal header 9.

The rim portion of the header is rolled or pressed with a channel shapedin cross section, and the glassbulb I0 is joined to the outer cylinderof the channel. Flexibility of the outer cylinder in a radial directionminimizes strains in the glass of the bulb at the seal and thermallyisolates this seal glass cylinders each hermetically II, substantiallyui region from the glass-to-metal seals of the bushings 8.

There are no interelectrode spacers and the header, according to myinvention, comprises the sole support for the grid and cathode electrodeassemblies, and although the header is made of thin sheet metal it willrigidly hold the electrodes in their position in the tube and willwithstand warping caused by heat and at-. mospheric pressure, whichpressure may be upward of pounds on a header only 3.5 inches indiameter. I propose, according to my invention, to concave the headerinwardly as shown. The re-entrant concavity of the header not onlystrengthens the header but provides a convenient protecting recess forthe lead-in bushings 8. One convenient way to make my novel header is tospin or press the sheet material with a substantially hemispherical orconical portion I2 and with the channel I I along the rim of thehemisphere. Die punches may then be used to flatten seats for thebushings 8 in the bottom portion of the header. The exhaust tube I3 isjoined to the center of the bottom of the header, the sheet metal aroundthe exhaust tube being further stiffened by an embossed annular groovearound the exhaust tube junction. My header is easily made fromrelatively light weight sheet metal and without the usual heavyreinforcing metal plate across the end of the tube. The electrodes maybe supported directly on the header with no bracing means orelectrode-toenvelope spacers and with negligible displacement of theelectrodes during manufacture and use. 1

The screen grid is supported at the small end of the metal cone I4which, at its larger end, is slipped over the rim portion of the headerand into the channel I I and spot welded. The screen grid cone iscoaxial with the electrodes, and, with the metal header 9, completelyencloses the lead-in conductors for the cathode and control grid andshields these conductors from the anode.

The cathode support rod 5 is inserted at its lower end in an eyelet I5which is held against the upper side of the insulating bar I6 of thebridge structure 6 and is drawn as best shown in Figure 2 in snugcontact with the bar by metal strap I'I drawn tightly over the head ofthe eyelet by thebolt I8 with a tapered head and. tapered washer. As thebolt is tightened the strap is drawn downwardly and into the taperedhole in the ceramic. Opposite ends of the bar I 6 are bolted to clampsengaging the cathode lead-in conductors I just inside the header. Theheating circuit for the cathode is completed from one conductor throughthe heat shield I9, through the support rod 5, through the heatingcathode 4 and thence through the other conductor I insulatingly joinedto the heat shield by the ceramic bushing 2|. The heat shield I9, beinglarger in diameter than the small end of the cone, cooperates with thecone to prevent heating, by the cathode, of the bridge structure 6 andor the glass-to-metal seals of the lead-in bushings l.

The anode may be cooled according to my invention with an air radiatorcomprising fins II integrally joined to a hub 22 which in turn may beshrink-fitted by diiierential expansion on a sleeve 28. The sleeve 23 isthen soldered to the outer surface of the anode to provide a lowresistance heat conducting band between the anode and the fins. Theradiator fins and hub may be machined from aluminum or other good heatconducting material and the sleeve and anode wall made, preferably, ofcopper.

The washer-like disc or collar 24 at the upper end of the control grid 3is provided with a series of holes circularly arranged to receive theends of the control grid wires. To obviate buckling or bowing of thesewires because of unequal I claim:

1. An electron discharge device comprising a cup-shaped anode, adish-shapedsheet metal header, a glass bulb hermetically joined to therim of the anode and to the rim of the header, a cathode, a control gridand a screen grid coaxial with and in said anode, lead-in conductorshermetically and insulatingly sealed through the bottom of said headerand connected to said cathode and control grid. a metal cone coaxialwith said anode and surrounding said conductors, the small end of thecone being joined to one end of said screen grid and the large end ofthe cone being joined to said header.

2. An electron discharge device comprising an envelope closed at one endwith a round sheet metal header, said header being relatively large indiameter and its sheet metal being relatively thin, said header beingdish-shaped, the bottom portion and the rim portion of the header beingjoined by a substantially conical shaped portion heat expansion, thewires are passed freely through the holes in the washer, the washerbeing held in place by tabs welded to only two or three of the gridwires. A metal or ceramic washer was found unsuitable because ofdifliculty in obtaining free movement of the wires through the holes inthe washer without either binding or excessive looseness. It has beenfound that a graphite or carbon washer ideally meets the requirements ofthe spacing collar. Graphite is sufliciently refractory to withstand thehigh temperatures and willnot bind the grid wires when hot.

The entire tube assembly may conveniently be supported upon a plate 25with a large central opening to clear the lead-in bushings I. Electricalconnection to the header and to its attached screen grid is made by anumber of flexible spring fingers 26 fastened as by spot welding to theupper surface of the plate and arranged around the periphery of theheader. The header and its connected screen grid is grounded for radiofrequency potentials by capacitively coupling the header to ground. Athin fiat insulator 28, approximately coextensive with the rim of theheader, separates the plate 2! from the metal plate 21, of the groundedtransmitter chassis.

Good results, according to my invention, have been obtained in makingtransmitter tubes of the type commercially known as the 827R, where thehigh frequency output power is one kilowatt at 108 megacycles or 1.5kilowatts at 50 megaoycles. The diameter of the anode is about 1.5inches, the anode length 2.25 inches, the header outside diameter 8.6inches, the overall length of the tube 4.5 inches, and the header ofcommercial .030 inch nickel-iron-cobalt alloy sheet. The filamentcarries 25 amperes and operates at about 2000 K. The upper part of coneI I, the

grid wires and metal parts adjacent the filament are preferably oftantalum, molybdenum or other highly refractory metal.

The dish-shaped contour of the header materially strengthens the headeragainst flexure and thus holds the cathode and control grid electrodesin place, and the length of the lead-in conductors is reduced withoutreducing the length of any of the insulating paths. My improved radiotube is easily made, the electrodes are accurately aligned andrigidlysupported, and the input electrodes are completely shielded fromthe output electrodes.

so that the header can withstand atmospheric pressure without fiexure,lead-in conductors insulatingly sealed in and extending through saidbottom portion of the header, a first electrode in and in spacedrelation with said envelope, the support for said first electrode beingsaid conductors and the sole support for said header being a hermeticjunction between the rim of said header and said envelope, 9. secondelectrode mounted in spaced cooperative relation with said firstelectrode.

3. An electron discharge device comprising a cup-shaped anode, a sheetmetal header hermetically closing one end of said anode, a cathode and agrid coaxial with and in said anode, leadin conductors hermetically andinsulatingly sealed through the bottom of said header and connected tosaid cathode, a metal cone coaxial with said anode and surrounding saidconductors, the small end of the cone being joined to said grid and thelarge end of the cone being joined to said header, a disc-shaped metalshield supported by said lead-in conductors in the cone andtransverselyof the axis of the cone, said disc being larger in diameterthan the small end of said cone and extending to but spaced from thewall of said cone.

4. An electron discharge device envelope comprising a header closing oneend of said envelope, said header comprising a round sheet metal member,said member being concave'd and reentrant with respect to said envelope,the bottom portion of the member being joined to the rim portion of theheader by'a substantially conically shaped portion, said rim portionbeing formed with an annular channel U-shaped in cross section, lead-inbushings hermetically sealed to said bottom portion of the header andsaid envelope being hermetically joined to the outer wall of saidchannel.

5. An envelope, a helical wire cathode in said envelope, two relativelyheavy support and current supply conductors through the envelope, asupport rod centrally in said cathode, means supporting said rodcomprising a bridge structure clamped at opposite ends to said lead-inconductors, said bridge structure being electrically non-conductivebetween its ends, said rod being clamped to the central portion of saidstructure, and electrical connections between the terminals of thecathode and said two conductors.

ARTHUR, K. WING, JR.

